1. Field of the Invention
The invention relates to a heating control of a fixing unit of an image recording apparatus.
2. Related Background Art
Hitherto, in a fixing unit which is installed in a recording apparatus of a laser beam printer or the like, a halogen heater or ceramic heater is used as a heat source, a temperature of a heat generated from the heat source is detected by a temperature sensor provided in the fixing unit, and a fixing temperature is controlled on the basis of temperature information. Further, in recent years, a fixing unit having two or more halogen heaters in order to reduce a warming-up time of the fixing unit has also been proposed.
In the recording apparatus equipped with such a kind of fixing unit, in what is called a standby mode other than the time of the recording operation, when a recording operation instruction is received, the fixing unit is controlled so as to be maintained at a predetermined temperature in order to promptly fix toner onto a transfer material. In a printing mode, when a detection temperature of a fixing roller detected by the temperature sensor is higher than a predetermined temperature, the heat source is turned off and when the detection temperature is lower than the predetermined temperature, the heat source is turned on, thereby performing a temperature control and keeping the fixing unit at a predetermined temperature.
The above conventional apparatus, however, has the following problems. That is,
(1) When the halogen heater is used as a heat source and an illuminating equipment to which a power source is supplied from the same-AC outlet as that of the recording apparatus exists, there is a problem such that an adverse influence is exerted on the illuminating equipment at the start of the heating of the fixing unit in dependence on an impedance of a power source line, so that the illumination momentarily becomes dark.
That is, in the standby mode after completion of a warming-up process of the fixing unit or during the printing operation, for example, when a plurality of halogen heaters are concurrently turned on or the on/off operations of the halogen heater are frequently repeated, there is a problem such that a fluorescent lamp to which a power source is supplied from the same AC outlet flickers or the like, in other words, there occurs a flicker phenomenon due to a rash current generated at the start of the heating of the heat source.
(2) In a fixing unit having a plurality of heat sources, since the temperature control is performed by using only one of a plurality of heat sources in the standby mode in order to suppress the maximum electric power consumption, there is a problem such that it is difficult to realize a long life of the fixing unit. Particularly, there is also a recording apparatus such that almost of the mode during the power-on is the standby mode. In such a case, since the life of the fixing unit is fairly short, there is a problem such that the number of times of replacement of the fixing unit increases and the use efficient is bad.
(3) Since a plurality of heat sources are simply turned on and off on the basis of the predetermined temperature as a reference during the printing operation, particularly, in a high speed printer using a heat source of a high power, since a recording paper absorbs a large quantity of heat from the fixing unit, a temperature rising speed at the time of turn-on of the heat source and a temperature decreasing speed at the time of turn-off of the heat source are large. There is, consequently, a problem such that a temperature change of the fixing unit Is also large and a high accurate temperature control cannot be performed.